1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a ferroelectric recording medium, and more particularly, to a multi-bit ferroelectric recording medium and a writing method for the same.
2. Description of the Related Art
Ferroelectric material has spontaneous polarization that can be reversed by an electric field. A ferroelectric recording medium is a high-capacity nonvolatile recording medium on which data can be written, modified, and stored using physical characteristics of the ferroelectric material.
A ferroelectric recording medium is disclosed in Japanese Patent Laid-Open Publication No. 2002-175602. A related art ferroelectric recording medium will be described with reference to FIGS. 1 and 2.
FIG. 1 is a perspective view of a related art ferroelectric recording medium, and FIG. 2 is a perspective view of another related artferroelectric recording medium.
Referring to FIGS. 1 and 2, related art ferroelectric recording mediums include a ferroelectric recording layer 2 (12). Using a read/write head 1 (11), data are read from or written to the ferroelectric recording layer 2 (22). The ferroelectric recording mediums may further include a separate protective film 13 (FIG. 2) so as to protect the read/write head 1 (11) and the ferroelectric recording layer 2 (22) from being damaged by a direct contact therebetween.
The ferroelectric recording layer 2 (22) is partitioned into a plurality of domains 3 (14). Data is recorded in each of the domains 3 (14) and read therefrom whenever necessary. A reading/writing method for a related art ferroelectric recording medium will now be described with reference to FIG. 3.
Referring to FIG. 3, a related art ferroelectric recording medium includes a ferroelectric recording layer 22 partitioned into a plurality of domains 24, 25, 26 and 27, and a protective film 23 for protecting the ferroelectric recording layer 22.
When a predetermined voltage is applied to a specific region of the ferroelectric recording medium through a read/write head, a polarization reversal occurs in a corresponding domain and then the domain is switched back to the original polarization by another voltage.
Thus, an upper polarization and a lower polarization occur in each domain 24, 25, 26 and 27 of the ferroelectric recording layer. States of the domains 24, 25, 26 and 27 are defined by the upper polarization and the lower polarization.
When the read/write head is positioned above a specific domain in which information is recorded, an induced current corresponding to the polarization of the domain is generated from the read/write head. Reference symbols V1 and V2 represent polarization amounts, and reference symbols I1 and I2 represent induced currents respectively corresponding to the polarization amounts (V1≠V2).
The related art ferroelectric recording medium can have only two states. That is, the upper polarization and the lower polarization in each domain and can store only one bit in each domain. Accordingly, there is a demand for improving the ferroelectric recording medium so that the ferroelectric recording medium can have more states and more bits can be recorded in each domain.